1. Technical Field
The present invention relates to a heating apparatus using a burner, especially to a heating apparatus for heating water provided with a heat exchanger adapted to utilize (recover) latent heat of combustion gas.
Herein, in the present application, the term “water” includes cold water and hot water, if not otherwise specified.
2. Background Art
A heating apparatus (also called a heat source equipment) using a burner for burning gas or liquid fuel is commonly used as heat source for a device such as a water heater or a bath heater. Recently, a combustion-type heating apparatus having higher heat efficiency than the conventional one has been desired in the point of view of energy saving or environmental conservation. Therefore, in order to achieve the above-mentioned object, a combustion-type heating apparatus provided with a plurality of heat exchangers or a heating apparatus of the combustion type referred to as “of the latent heat recovery type” or “of the latent heat use type”, which can utilize (or recover) not only sensible heat of combustion gas but also latent heat thereof, has been proposed.
The conventional combustion-type heating apparatus of the latent heat recovery type has such a configuration as disclosed in a patent document 1 listed below, for example, and has a heat exchanger for sensible heat mainly transferring sensible heat of combustion gas to water supplied to the apparatus and a heat exchanger for latent heat mainly transferring latent heat of combustion gas to water supplied to the apparatus (also transferring the remaining sensible heat to the water).
FIG. 17 is a model diagram of a combustion-type heating apparatus of the latent heat recovery type described in the patent document 1, which uses a finned tube 200 as a latent heat exchanger. Herein, the finned tube 200 is a heat receiving tube around which fins are welded and also called a fin tube.
In the art, the finned tube 200 is directly inserted into a combustion gas passage 201. Specifically, in the art, a wall 202 defines the combustion gas passage 201, into which the finned tube 200 is inserted, as shown in FIG. 17. In the art, the finned tube 200 in the passage 201 is a tube bent and serially arranged.
On the other hand, heating apparatus (heat source equipment) provided with a plurality of functions such as a hot-water supply function and an air heating function or a function of heating water of the bath again are in widespread use. Most of these types of heating apparatus each have a plurality of heat exchange circuits, as exemplified by a heating apparatus employing a so-called two-burner and two-water passage system, as disclosed in the patent document 2 listed below.
Patent Document 1: JP 11-148642A
Patent Document 2: JP 2003-4227A